1. Field of the Invention
The present invention relates generally to a planarization apparatus and method, and more particularly to a planarization apparatus and method for planarizing the reverse of a semiconductor wafer on which no chip is formed in a semiconductor wafer manufacturing process.
2. Description of Related Art
A planarization apparatus for grinding the reverse (one side) of a semiconductor wafer has chucks for holding the wafer by suction, a rough grinding wheel, a fine grinding wheel, a reverse cleaning unit, and the like. One chuck holds the obverse (the other side) of the wafer, and then the rough grinding wheel is pressed against the reverse of the wafer. The reverse of the wafer is roughly ground by rotating the chuck and the grinding wheel. The roughly-ground wafer is detached from the chuck and is held by another chuck for the fine grinding so that the wafer can be finely ground by the fine grinding wheel. The finely-ground wafer is transferred to the reverse cleaning unit so that the reverse of the wafer can be cleaned. That completes the grinding of the reverse of one wafer by the planarization apparatus.
The wafer whose reverse has already been ground is transferred from the planarization apparatus to an etching apparatus, which etches the wafer to remove a machining deteriorated layer formed at the reverse of the wafer.
If the wafer is ground into an extremely thin wafer close to a standardized article, the wafer is damaged (cracked or chipped) because of the machining deteriorated layer when the wafer is transferred from the planarization apparatus to the etching apparatus.
To address this problem, the conventional planarization apparatus grinds the wafer to such a thickness as not to damage the wafer during the transfer. With respect to the thickness of the wafer, the planarization apparatus roughly grinds the wafer with the thickness of 725 μm sliced from an ingot to the thickness of 250 μm, and finely grinds the wafer to the thickness of 200 μm. The wafer is machined to the standardized thickness of 50 μm at the etching step.
The conventional planarization apparatus, however, cannot grind the wafer close to the standardized thickness in order to prevent the wafer from being damaged during the transfer. For this reason, a machining allowance (150 μm in the above example) is large at the etching step. Thus, it takes a long time to etch the wafer, and the throughput cannot be improved.